Generally, a fluid powered systems use hydraulic pressure and flow to provide the required fluid power to the system. Such systems rely on a hydraulic pump to provide pressurized fluid which is then regulated and controlled by a valve system comprising one or more valves. The valve system regulates the pressure to release fluid pressure when it becomes too great which may cause damage to the pump and other systems. In addition, the valve system directs energy to various systems on demand.
A conventional vane-type pump comprises a cam (pump) ring having a substantially elliptical cam surface, a rotor which is adapted to rotate within the cam ring and a plurality of vanes adapted to move back and forth within radial slits formed in the rotor. The cam ring is stationary and the outer edges of the vanes touch the inside of the surface of the cam ring. Because of the substantially elliptical shape of the cam ring, the vanes slide in and out of their slots and maintain contact with the inside surface of the cam ring as the rotor turns therein. The volume of each pumping cavity constantly changes due to the elliptically shaped cam ring. Volume increases as the vanes move through the rising portion of the cam ring, drawing fluid through an intake port. When the vanes move into the xe2x80x9cfallingxe2x80x9d portion of the ring contour, the volume decreases and forces the fluid out through the discharge ports. An intake portion of the hydraulic pump receives low-pressure hydraulic fluid from a pump reservoir. Discharged fluid, under high pressure, flows to a desired system location. In the case of an automotive fluid power system, for example, the desired system location may be a steering system to provide power assist steering.
In fixed-displacement pumps, at low engine speeds, the operating system can handle the volume of hydraulic fluid provided by the pump. Since the pump is usually directly driven by the crankshaft, line pressure dramatically increases at higher engine speeds because the pump draws and discharges a greater volume of fluid per unit time as it runs faster. These conditions raise operating temperatures and reduce pump durability and operating life. The system lines and seals are also strained. In addition, the torque necessary to drive the pump increases at higher system back pressures which corresponds to additional horsepower (energy) being required to effectively overcome the system back pressure and distribute the fluid throughout the system, thereby wasting fuel to generate unneeded line pressures.
A common prior art solution for fixed-displacement pumps has been to rely on the valve system to xe2x80x9cshort-circuitxe2x80x9d the flow from the high-pressure side to the low-pressure side of the system at excessive operating pressures. Another pump conventionally used is a variable-displacement pump. A variable-displacement pump provides a reduction in flow as a function of operating conditions and therefore requires more costly shaft support solutions. Additionally, since variable-displacement pumps are typically single stroke, the pumps require a larger package size to provide the same pumping capacity. Variable-displacement pump valving also make these pumps less efficient in the full displacement operating condition.
Disclosed herein is a hydraulic pump comprising a housing, a primary discharge outlet, an auxiliary discharge outlet, a flow control valve, a first fluid passageway within the housing passing fluid from a first discharge port to the primary discharge outlet, a second fluid passageway within the housing passing fluid from a second discharge port to a common port of the flow control valve, a third fluid passageway within the housing passing fluid from a first switched port of the flow control valve to the auxiliary discharge outlet, and a fourth fluid passageway within the housing connecting a second switched port of the flow control valve to the primary discharge outlet. The primary discharge outlet and the auxiliary discharge outlet are each adapted for connection with external lines of a hydraulic system.
The above-described and other features and advantages of the disclosed hydraulic system will be appreciated and understood by those skilled in the art from the following detailed description.